public class Poly04 {
    public static void main(String[] args) {
        Sub sub=new Sub();
        System.out.println(sub.count);
        sub.display();
//        =左侧是编译类型，=右侧是sub是运行类型

        Base base=sub;
        System.out.println(base==sub);
        System.out.println(base.count);
        base.display();
    }
}
